JPH02250999A - Method for coating aluminum wheel - Google Patents

Abstract

PURPOSE:To form a transparent coating film excellent in edge covering property and characteristics by coating an aluminum wheel with a specific anionic electrodeposition paint contg. fine powder silica and then applying a specified thermosetting acrylic resin paint. CONSTITUTION:An aluminum wheel is electrodeposition-coated with an anionic electrodeposition paint contg. 100 pts.wt. of a thermosetting resin having >=30% (20 deg.C) elongation percentage and -25 to 60 deg.C glass transition temp. and 5 to 35 pts.wt. of transparent fine powder silica with 5mmu to 5mu particle diameter. The thermosetting resin is preferably composed of a base resin, such as acrylic resin and a curing agent such as melamine resin. The paint is preferably applied in about 10 to 50mu cured film thickness, heated at about 130-170 deg.C, and cured. A thermosetting acrylic resin capable of forming a coating film having 3 to 30% (20 deg.C) elongation percentage and 60 to 130 deg.C glass transition temp. is applied on the electrodeposition-coating film in about 20-80mu film thickness. By this method, a coating film excellent in edge covering property, transparency, impact resistance, weather resistance, smoothness, adhesion, physical properties, etc., is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating method for wheels (hereinafter abbreviated as "aluminum wheels").

Traditionally, automobile wheels were mainly made of steel, but
In recent years, aluminum and aluminum alloy castings are being replaced, as they are lighter in weight, have superior corrosion resistance, and are attractive in design. The aluminum wheel is coated with one or more coats of transparent or colored organic solvent-based thermosetting acrylic resin paint to improve its cosmetic properties and weather resistance. .

However, aluminum wheels have many sharp protrusions to improve their design, and when such materials are painted with the above-mentioned conventional acrylic resin paints,
Although the cosmetic properties of flat areas are improved, paint flows on sharp, sharp areas (hereinafter sometimes referred to as ``edges'') during baking, resulting in the formation of a paint film ( (As a result, thread-like rust occurs and progresses from the edges, resulting in a significant loss of aesthetic appeal.) The solution to these defects is to polish the edges to eliminate sharp corners. Although it is effective, it is difficult to incorporate into the production line because it takes too many man-hours, and polishing itself may not be desirable in terms of design.Furthermore, paint for aluminum wheels has a unique design feel. Another limitation is that it is difficult to incorporate color pigments that inhibit the transparency of the coating film in order not to impair the transparency of the coating film.

Therefore, the present inventors solved the above-mentioned defects, and the paint applied to the edge part does not flow during baking, and the paint film formation property on the edge part is good, and it also has transparency, impact resistance, weather resistance. We conducted intensive research with the aim of developing a coating method for aluminum wheels that forms a coating film with excellent properties such as smoothness, smoothness, adhesion, and physical properties.

As a result, by applying an undercoat of an anionic electrodeposition paint containing a specific amount of ultrafine powdered silica to a thermosetting resin with excellent flexibility, and then applying a topcoat of a thermosetting acrylic resin paint with a specific composition. The above object has been achieved and the present invention has been completed.

That is, 1 the present invention has (A) an elongation rate of 30% (20°C)
As described above, an anionic electrodeposition paint containing 2 to 35 parts by weight of transparent finely powdered silica with a particle size of 5 mμ to 5 μ per 100 parts by weight of a thermosetting resin having a glass transition temperature of 125 to 60°C was used. Coating, then (B) elongation rate of 3 to 30
% (20°C) and a glass transition temperature of 60 to 130°C.

The feature of the present invention is that aluminum wheels are
), and as a result, all of the above-mentioned defects were eliminated and the objective was achieved. In other words, the coating film made of paint (A) has extremely excellent flexibility and adhesion because it contains a resin having the above-mentioned specific physical properties as an essential component, and therefore, even if it is hit by a pebble or the like while driving, its energy will be absorbed. is absorbed into the paint film to prevent cracking and peeling, and no thread rust is observed. Also, since it also contains a specific fine powder, the electrodeposited paint film with paint (A) can be prevented. exhibits significant thixotropy and low thermofluidity. Moreover, even if the coating film is baked at a high temperature to harden it, the coating material (A) especially applied to the edge portions is hardly thermally fluidized, so that the edge portions are coated with excellent properties.

If the above-mentioned fine powder is not blended, the viscosity and thixotropy of the applied coating material are low and the fluidity is large, so that it will flow under heat during the baking process and coating the edges can hardly be expected.

Moreover, the paint (B) has excellent adhesion with the paint (A),
Moreover, it has good weather resistance, hardness, flexibility, and durability.

As a result, the coating film obtained by the method of the present invention, which is obtained by applying the above-mentioned paints (A) and CB), has improved edge coverage of the aluminum wheel, and almost no occurrence of base steel etc. is observed from those areas. Moreover, since the coating film formed can be colorless and transparent, it does not interfere with the unique metallic feel of Ualmini Mu, and it also has excellent smoothness, weather resistance, adhesion, and physical performance.

Next, the method of the present invention will be explained in more detail.

Aluminum wheel: An automotive wheel made of aluminum alloy casting, which is the object to be coated in the painting method of the present invention, and is often subjected to shot-O-last treatment and cutting. After that, chromium-based and non-chromium-based chemical conversion treatment (
surface treatment).

Paint (A): 2 parts of transparent fine powder silica with a particle size of 5 mμ to 5μ per 100 parts by weight of a thermosetting resin with an elongation rate of 30% or more (20°C) and a glass transition temperature of 120 to 60°C.
This is an anionic electrodeposition paint containing ~35 parts by weight, which is applied to the aluminum wheel by electrodeposition prior to paint (B) described later.

The thermosetting resin used in the paint (A) has a high elongation rate and glass transition temperature (Tg) of a cured coating film made only of the resin.
must be within the above range. That is, the elongation rate is 30% or more at 20°C, preferably 50 to 600%, more preferably 100 to 400%,
Tg is in the range of -25 to 60°C, preferably -20 to 55°C, more preferably -1O to 50°C. A coating film whose essential component is a resin with an elongation rate and Tg within this range has good flexibility and adhesion, and is almost free from thread rust (and will not crack or crack even if a pebble hits it). It can prevent the occurrence of peeling, etc., and can be used in environments with high temperatures, low humidity, or high humidity.
Almost no deterioration of adhesion is observed even when the humidity changes to low. Therefore, the elongation rate may deviate from the above range, or the Tg may be 60°C.
If the Tg is higher, adhesion will deteriorate in an environment where humidity and temperature change rapidly, while if the Tg is lower than -25℃, the coating film will be too soft and easily scratched by collisions with pebbles, which poses a practical problem. .

First, thermosetting resin is a composition that undergoes a three-dimensional cross-linking and curing reaction at room temperature or by heating, and is mainly composed of a base resin and a curing agent, and the elongation rate of the reaction-cured product (coating film) of both components is and Tg must be within the above range.

Specifically, acrylic resins, melamine resins, urea resins (including methylol compounds and alkyl ether compounds), polyisocyanate compounds (including blocked compounds), epoxy resins, etc. can be used as the base resin.

Among these, weather resistance.

Acrylic resins, polyester resins, and the like, which have excellent transparency, are suitable.

Adjustment of the physical property values within the above range by the thermosetting resin can be easily carried out by appropriately selecting the composition of both components, the amount of crosslinkable functional groups, the blending ratio, the curing method, etc.

Next, the finely powdered silica used in the paint (A) is
) to suppress the thermal flow of the electrodeposited coating film.
The particle size is 5 mμ to 5μ, preferably 5 to 50 mμ (0,0
05-0:05μ), particularly preferably 5-23μ
It is a fine powder containing 90% by weight or more of (0,005 to 0.023 u). Here, silica is called fine powder silicic acid or white carbon, and is known as an extender pigment that is added to paints.
If it is smaller than 5μ, the viscosity and thixotropic property will be too high, and the production and painting workability of the paint will be significantly reduced.On the other hand, if it is larger than 5μ, the thixotropic property will be reduced and the edge coverage will be insufficient. Therefore, neither is preferable.

In addition, the blending amount of these fine powders is as follows:
2 to 35 parts by weight, preferably 15 to 25 parts by weight, per 00 parts by weight (solid content).

If the amount is less than 2 parts by weight, the edge coverage will not be sufficient, and if it is more than 35 parts by weight, the finished appearance will deteriorate, so both are not preferred.

The paint (A) is an anionic electrodeposition paint whose main components are the above-mentioned thermosetting resin and finely powdered silica.

When applying the paint (A), the solid content concentration in the paint is approximately 10 to
It is adjusted to 30% by weight and carried out by an anion electrodeposition coating method under conditions known per se.

Prior to coating with paint (A), the aluminum wheel may be subjected to a normal surface treatment as necessary. It is preferable to apply the coating to a thick layer and heat it at 130 to 170°C to cure it.

Paint (B): Elongation rate is 3-30% and Tg is 60-1
This is a thermosetting acrylic resin paint that forms a coating film at 30°C, and is applied to the surface coated with the paint (A). Specifically, it has the physical properties listed above, as well as finished appearance (sharpness, smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalking resistance, etc.), chemical resistance, and water resistance. It is a thermosetting acrylic resin paint that is known in itself and forms a coating film with excellent properties such as durability, moisture resistance, and hardening properties.
Dispersion) Any form such as liquid type, powder type, or high solid type can be used. For example, acrylic resins having one or more functional groups selected from hydroxyl groups, glycidyl groups, etc.
Suitable number average molecular weight is approximately to, ooo to 100,000, hydroxyl value is 15 to 100, and acid value is in the range of 0 to 15.)
Examples include the above-mentioned coating material which uses one or more selected from amino resins, urea resins, polyisocyanate compounds, block polyisocyanate compounds, etc. as a curing agent.

Paint (B) can be either an enamel paint in which metallic pigments and/or color pigments are blended into a paint mainly composed of the above-mentioned acrylic resin and curing agent, or a clear paint that does not contain any or little of these pigments. It may be of type.

For metallic finishes, metallic base 10
So-called 2CIB, which is painted to ~15μ and clear coated.
Generally, a method is used. In some cases, the coating is applied three or four times to improve edge coverage and finish.

The coating method for the paint (B) is preferably a spray coating method such as air spray, airless spray, or electrostatic coating.
The coating film thickness is 20 to 80μ, especially 25 to 80μ, based on the cured coating.
60μ is preferred.

Regarding the single coating film of the paint (B), the elongation rate is 3 to 30%,
It is important that the content is preferably in the range of 5 to 20%, more preferably 5 to 15%, and that the Tg is in the range of 60 to 130°C, preferably 60 to 110°C. Paint (B)
If the elongation rate of the coating film is less than 3%, the flexibility will be poor and cracking will occur easily. If it is greater than 20%, the coating film hardness will not be sufficient. On the other hand, if the Tg is lower than 60°C, the coating film will become soft. , higher than 120°C (both of which are unfavorable because the flexibility decreases).

The elongation rate (tensile elongation rate at break) of the coating film of paints (A) and (B) was determined using a universal tensile tester with a constant temperature bath (Shimadzu Autograph S-D model) for a sample with a length of 20 mm.
These are the values measured at +20°C and a tensile rate of 20a+a+/min.The samples used for these measurements were coated with the paint on a tin plate to a film thickness of 60μ based on the formed coating, and After baking at ℃ for 30 minutes, it was isolated by the mercury amalgam method.

In addition, the glass transition temperature of both paints is DAYNAMICV
ISCOELASTOMETERMODEL VIBR
ON DDV-11-EA type (TOYOBA CDWIN
CO, Ltd). Samples were prepared in the same manner as used for the elongation measurements described above.

According to the method of the present invention described above, the coating film formed on the aluminum wheel by the steps of coating the aluminum wheel with the coating material (A) - curing or non-curing - coating the coating material (B) - heating, the coating of the coating material (A) is omitted. Compared to coatings formed using conventional methods, it has better finished appearance (e.g. smoothness, gloss, sharpness, etc.) and water resistance, as well as impact resistance, edge corrosion resistance, physical properties, weather resistance, etc. It has the characteristic of being significantly improved.

Next, examples and comparative examples related to the present invention will be described.

Example 1 Aluminum alloy casting (1OOx 150
X8++us) was surface treated with Bonderite BT3753 (manufactured by Nippon Barker Co., Ltd., trade name).

The object to be coated is electrodeposited using the following anionic electrodeposition paint, and the water in the paint film is removed by air blowing, and then the thermosetting acrylic resin clear paint ([Magicron Clear] Kansai Paint ( Co., Ltd. parts name) painted with Soubreni,
Both coatings were cured by heating at 160° C. for 30 minutes.

Anionic electrodeposition paint: anionic acrylic resin/melamine resin/transparent powder silica (Note 1) =to.

/20/10 (solid content weight ratio), neutralized with amine, dispersed in water, and adjusted to a solid content concentration of 15% with deionized water.

(Note 1): Aerosil R-972 (manufactured by Nippon Aerosil Co., Ltd., trade name. Fine powder silicic acid, average particle size 16 mμ) Comparative Example 1 As an anionic electrodeposition paint, transparent fine powder silica was removed from that of Example 1. The same procedure as in Example 1 was carried out except for the following.

Performance test results As shown in Table 1.

Table 1 (2) Film thickness is measured for the formed (cured) coating film. 1) Elongation and Tg are measured by the method described above, and the units are % and °C, respectively.

Ta.

The film thickness on the edge part was determined by coating a replacement blade of an office cutter in the same manner as above, and observing the blade edge with a stereomicroscope at 120x magnification.
The thickness of the cured film formed on the cutting edge was measured.

(3) Resistance to sludge spray Resistance to sludge spray is measured by subjecting the painted blade (edge part) and the object to be coated (flat part) with the coating film cross-cut so as to reach the substrate for 500 hours. After that, the creep width (one side) from the edge portion and cross-cut portion was measured.

0: 211 tl or less 622-4 mm X: 41 m 01 or more (4) Yarn rust resistance: The above-mentioned object to be coated with two diagonal cuts made with a cutter to reach the substrate and the same as in (3) above. JIS Z2371 spare blades ±2℃, humidity 85±2
%) for 240 hours, and after 5 cycles of this process, the creep width (one side) from the cross-cut portion and edge portion was examined for the occurrence of yarn rust.

○: Creep width is 2 mm or less △: Creep width is 2 to 4 m ■ ×: Creep width is 4 mm or more Impact resistance: Performed in an atmosphere at 20°C according to JIS K5400-1979 6.13.3B method. Weight 500
Damage to the paint film is examined by dropping a 50cm weight from a height of 50cm.

○: No abnormality Δ: Slight cracking and peeling ×: Significant cracking and peeling July 1, 1999, Utah Date 1, Incident indication 1999 patent application No. 72966 Coating method for aluminum wheels 3, person making corrections Relationship to the incident Patent applicant address: 33-1 Kanzaki-cho, Amagasaki-shi, Hyogo Prefecture June 1, 1999
2nd (shipped on July 4, 1999) 5. Subject to correction

Claims (1)

[Claims] (A) 5 to 35 parts of transparent fine powder silica with a particle size of 5 mμ to 5 μ per 100 parts by weight of a thermosetting resin with an elongation rate of 30% (20 °C) or more and a glass transition temperature of -25 to 60 °C
(B) thermosetting acrylic to form a coating film having an elongation rate of 3 to 30% (20°C) and a glass transition temperature of 60 to 130°C; A method for painting aluminum wheels characterized by applying resin paint.